Sequential Star Formation in RCW 34: A Spectroscopic Census of the Stellar Content of High-Mass Star-Forming Regions

Abstract

In this paper, we present VLT/SINFONI integral field spectroscopy of RCW 34 along with Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different regions. A large bubble has been detected in the IRAC images in which a cluster of intermediate-and low-mass class II objects is found. At the northern edge of this bubble, an H ii region is located, ionized by 3 OB stars, of which the most massive star has spectral type O8.5V. Intermediate-mass stars (2-3 M ) are detected of G-and K-spectral type. These stars are still in the premain-sequence (PMS) phase. North of the H ii region, a photon-dominated region is present, marking the edge of a dense molecular cloud traced by H 2 emission. Several class 0/I objects are associated with this cloud, indicating that star formation is still taking place. The distance to RCW 34 is revised to 2.5 ± 0.2 kpc and an age estimate of 2 ± 1 Myr is derived from the properties of the PMS stars inside the H ii region. Between the class II sources in the bubble and the PMS stars in the H ii region, no age difference could be detected with the present data. The presence of the class 0/I sources in the molecular cloud, however, suggests that the objects inside the molecular cloud are significantly younger. The most likely scenario for the formation of the three regions is that star formation propagated from south to north. First the bubble is formed, produced by intermediate-and low-mass stars only, after that, the H ii region is formed from a dense core at the edge of the molecular cloud, resulting in the expansion similar to a champagne flow. More recently, star formation occurred in the rest of the molecular cloud. Two different formation scenarios are possible. (1) The bubble with the cluster of low-and intermediate-mass stars triggered the formation of the O star at the edge of the molecular cloud, which in its turn induces the current star formation in the molecular cloud. (2) An external triggering is responsible for the star formation propagating from south to north.

Sequential star formation in IRAS 06084-0611 (GGD 12-15)

“…Our findings show an interesting similarity to those found in the S255 complex (Bik et al 2010;Wang et al 2011). Also in this regions, a group of intermediate mass stars (up to a few Myr) seems to have formed after star formation in a smaller region containing younger, more massive stars.…”

“…The data reduction consists of correcting for dark, flatfield and distortion as well as reconstructing the final 3D data cubes (see Bik et al 2010 for a detailed description). The final reduced SINFONI data of IRAS 06084-0611 consist of 3D data cubes with two spatial (x − y) dimensions and a third dimension encompassing the H-and K-band (1.4-2.45 μ) spectra for each individual pixel.…”

“…Observational studies have started to map the interaction of high-mass stars and previously hidden stellar content in those star-forming regions (Blum et al 2000;Bik 2004;Alvarez et al 2004;Churchwell et al 2006). Much less ambiguous identification and classification of the stellar content has been demonstrated by the diagnostic power of near-infrared (NIR) spectroscopy (Hanson et al 2002;Bik et al 2005Bik et al , 2010Puga et al 2010;Martins et al 2010). A&A 531, A27 (2011) Fig.…”

“…5. This paper is the third in a program to obtain a full NIR spectroscopic census of the stellar content of a sample of high-mass star-forming regions by means of integral field spectroscopy using VLT/SINFONI. The first paper by Bik et al (2010) studies the star formation process in the high-mass star-forming region RCW 34. A spatial distinction between class II sources inside a "bubble region" on one hand, and the H ii region, the massive stars and the class 0/I sources in the molecular cloud on the northern edge of the bubble on the other hand, suggest that sequential star formation is at work from south to north.…”

Fast and accurate frequency-dependent radiation transport for hydrodynamics simulations in massive star formation

“…from the Spitzer Space Telescope Survey and millimeter interferometry, support the assumption that the basic concepts of star formation, including the collapse of an unstable gas and dust core, the formation of both bipolar outflows and jets, as well as accretion disks, are possibly valid throughout the whole range of stellar masses (e.g. Bally 2008;Bik et al 2008;Kumar & Grave 2008;Steinacker et al 2008;Vehoff et al 2008). A good review of observational results can be found for instance in Beuther et al (2007).…”